This invention relates to methods and apparatus for testing wells.
After a wellbore has been drilled, testing (e.g., drillstem testing or production testing) may be performed to determine the nature and characteristics of one or more zones of a formation before the well is completed. Characteristics that are tested for include the permeability of a formation, volume, pressure, skin, and temperature of a reservoir in the formation, fluid content of the reservoir, and other characteristics. To obtain the desired data, fluid samples may be taken as well as measurements made with downhole sensors and other instruments.
One type of testing that may be performed is a conventional drillstem test. A drillstem test is a test taken through the drillstem by means of special testing equipment attached to the drillstem. The special equipment, which may include pressure and temperature sensors and fluid identifiers, determines if fluid components in commercial quantities have been encountered in the wellbore. The fluid components are normally then produced to the surface and are either flared or transported to storage containers. Producing the fluid components to the surface at the testing stage, and particularly flaring the fluid components at the surface, creates a potential environmental hazard and is quickly becoming a discouraged practice.
Another type of testing that may be performed is a closed-chamber drillstem test. In a closed-chamber test, the well is closed in at the surface when producing from the formation under test. Instruments may be positioned downhole and at the surface to make measurements. One advantage offered by closed-chamber testing is that hydrocarbons and other well fluids are not produced to the surface during the test. This alleviates some of the environmental concerns associated with having to burn off or otherwise dispose of hydrocarbons that are produced to the surface. However, conventional closed-chamber testing is limited in its accuracy and completeness due to limited flow of fluids from the formation under test. The amount of fluids that can be produced from the zone under test may be limited by the volume of the closed chamber.
A further issue associated with testing a well is communication of test results to the surface. Some type of mechanism is typically preferred to communicate real-time test data to well surface equipment. One possible communications mechanism is to run an electrical cable down the wellbore to the sensors. An alternative to real-time data gathering is to utilize downhole recorders that record the downhole sensor data and are subsequently retrieved to the surface after the test.
In addition, when testing is conducted in a cased wellbore, the casing must be perforated in order to flow the hydrocarbons into the wellbore. Perforating methods used to perforate the appropriate zones include wireline and tubing conveyed perforating. If tubing conveyed, the perforating guns are run downhole attached to the testing instruments. If wireline conveyed, the perforating guns are run first, and the testing instruments are deployed downhole once the guns are removed from the wellbore. The perforating jobs tend to be more intricate if more than one zone needs to be perforated within the wellbore.
A need thus exists for an improved method and apparatus for testing wells.
One embodiment of my invention comprises a tool string for testing a wellbore formation that includes a production inlet, an injection outlet, and a sampler apparatus. Fluid is taken from a production zone, into the tool string through the production inlet, out of the tool string through the injection outlet, and into the injection zone. Within the interior of the tool string, the sampler apparatus takes samples of the fluid flowing therethrough. In another embodiment, a large volume of sample fluid is trapped within the interior of the tool string, such as between two valves, and is removed from the wellbore along with the tool string subsequent to the test. In another embodiment, the tool string includes at least one perforating gun to perforate one of the production and injection zones. The tool string may also include two perforating guns to perforate both the production and injection zones. One of the two perforating guns may be an oriented perforating gun so that upon activation the shape charges do not disturb any of the cables, data lines, or transmission lines associated with the tool string.